Lubricant composition



United States Patnt fornia Research Corporation, San Francisco, Calif., a corporation :of Delaware NqjDraWing. Original application February 3, 1956, Serial No. 563,207. Divided and this application Match 14, 1957, Serial N0. 645,893

4 Claims. (Cl. 2 52-56) This invention relates to a novel lubricant composition, and it is particularly directed to the provision of a lubricant composition which is adapted to be employed in internal combustion engines.

With the refinements now being made in automotive and other internal combustion engines, a great deal of attention is being directed to the provision of a lubricant which will permit the engine to be operated at a high level of efiiciency over long periods of time. The primary function of the lubricant is, of course, to reduce friction and thereby not only decrease the wear on pistons, piston walls, bearings and other moving parts, but also increase the eificiency of the engine. Additionally,

a it is also a function of the lubricant to prevent the deposition of solid products on the piston walls and other surfaces of the engine coming in contact with the lubricant. Such deposits seriously interfere with efiicient engine operation for they accelerate piston ring and cylinder wall wear and also increase oil losses by plugging the oil ring grooves. The troublesome deposits which form on the face of the piston and on the other walls of the combustion chamber, as well as on valves and spark plugs are also partially attributable in many cases to the lubricant, and especially to various of the metal-containing additives employed therein. It is of importance to eliminate or at least minimize the formation of all such deposits, and it is the basic object of this invention to achieve such a result.

To a minor degree, certain of the deposits formed on engine surfaces have their origin in the oil itself, that is to say, in the decomposition products of the oil. A more important, though still minor, source of engine deposits lies in the additives with which oils are conventionally supplied. This is particularly the case with metal-containing additives as, for example, the organic, metal-containing salts which are incorporated in the oil to increase the detergency thereof, and the various metalcontaining compounds which are added to increase the lubricity of the oil and reduce piston ring and cylinder wall wear. Whenever oil is burned in the engine (as occurs with the oil film present in the cylinder wall during the combustion stroke) any metal-containing additives present in the oil may form an ash which is partially deposited out on the various surfaces of the combustion chamber and on those of the spark plugs and valves. Accordingly, it is a particular object of this invention to provide a lubricant composition which is compounded with metalor mineral-free detergents and wear-reducing additives.

While certain of the additives heretofore employed in oils (and to a lesser degree the oil itself) are partially responsible for deposits which form on engine surfaces, it is now recognized that the major source of such deposits or their precursors lies in the various aldehydes, acids, oxy-acids and other similarly reactive, partiallyoxidized combustion products of the fuel. These products are formed both under pre-ignition conditions as well as during the combustion step proper, particularly during the period before the engine has reached operating temperature. Accordingly, under city driving conditions where the engine is repeatedly started in the cold condition and is seldom driven for a distance sufficient to reach the most, efficient operating temperatures, the formation of partial oxidation products is particularly severe. Many of these partial oxidation products are carried down into the crankcase of the engine along with other blow-by gases, and since most are insoluble or only sparingly soluble in lubricating oils, they tend to separate from the oil and adhere to engine surfaces or form large droplets. In either case, under the elevated temperature conditions prevailing in the engine, these reactive monomers quickly polymerize to form solid masses which readily deposit out on the engine wall surfaces.

It is the practice in the art to prevent the formation of such deposits by adding to the lubricant a material normally referred to as a detergent. Insofar as is known, all the detergent additives which have heretofore been successfully employed on a commercial scale are organic, metal-containing compounds such as calcium petroleum sulfonate, calcium cetyl phosphate, calcium octyl salicylate, calcium phenyl stearate, the barium salt of waxsubstituted benzene sulfonate, or the potassium salt of the reaction product of phosphorus pentasulfide and polybutene. Various of these detergents act by reacting chemically with deposit precursors to form harmless compounds. Othersact to prevent flocculation or coagulation of solid particles in the oil and maintain the same in a state of suspension as finely divided particles. Still others not only perform this dispersant function but also effect the solubilization or emulsification of the sparingly soluble monomers in the oil and thereby greatly reduce the rate of polymerization. In the latter case, such polymer materials as do then form within the body of the oil are smaller in size and can be peptized or dispersed in the oil much more readily than is the case with the large polymeric particles which are formed on exposed engine surfaces or in droplets lying without the oil.

Detergents capable of acting in the latter fashion are preferably employed wherever possible, particularly in automotive engines to be operated under city driving conditions. However, even among the metal-containing additives, few are available which are capable of solubiliziing any appreciable amount of all the many types of polymer precursors which are carried into the oil from the fuel. Accordingly, it is a more particular object of this invention to provide a lubricant composition incorporating a metal-free detergent which is capable of solubilizing or emulsifying in the lubricant large amounts of all the various partial oxidation products of the fuel which are carried into the oil, and which is also capable of maintaining in suspension in the oil the various solid polymeric materials which are present therein.

The problem of piston ring and cylinder wall wear, especially the control thereof, is also one which is closely related to the composition of the crankcase lubricant. Aside from abrasive wear, which is caused by dust and dirt and can be remedied by suitable filtering and aircleaning means, a large part of the wear experienced by piston ringsand cylinder wall is attributable to chemical attack by moisture and acidic products originating as by- 7 products of fuel combustion. I In engines operated at optimum temperature levels, these combustion products are largely discharged through the exhaust and breather pipe. However, under the relatively cold conditions experienced in city driving, and especially at cylinder wall temperatures below about 150 F., the moisture and acid products are condensed on the engine surfaces where they promote corrosive attack and are in a position to work past the piston and accumulate within the engine and in the crankcase oil. Thisdifi'iculty is one which the art has heretofore met most successfully by supplying the lubricating oil with additives such as the various metal salts of petroleum sulfonic acids and other metal-organic compounds, especially those having a basic reaction. However, this practice has a disadvantage of adding still another metal-containing ingredient to the oil and therefore of increasing the depositforrning characteristics of the lubricant composition. Accordingly it forms still another object of this invention to provide a lubricant c om position containing a metalor mineral-free additive which effectively decreases the wear experienced by piston rings and cylinder walls, particularly during periods before the engine has become thoroughly warmed to operat ing temperatures.

The present invention is based on the discovery that certain copolymers, which contain no metal component and therefore are substantially free of any ash-forming tendency, have the ability to impart excellent detergent and antiwear qualities to lubricating oils employed in internal combustion engines. In particular, these co polymers have the ability to solubilize in the oil large amounts of all the various partially oxidized combustion products of the fuels employed in internal combustion engines, while also having the ability of maintaining in a state of suspension any solid polymeric products present in the oil. Additionally, the copolymeric additives of the present invention effectively reduce the wear experienced by piston rings and cylinder wall surfaces even under the most unfavorable operating conditions such as are experienced during the starting and warming up of the engine. These additives have the advantage that they do not combine chemically with the various polymer precursors which are solubilized or dispersed in the oil, nor apparently do they act by a neutralization reaction in counteracting the effect of the various acidic fuel combustion by-products. Accordingly, they are capable of giving excellent protection against engine deposits and wear over extended operating periods. It should also be noted that the copolymeric additives of this invention are noncorrosive to the various bearing metals employed in engines.

Since the additives of the present invention difier in kind from any heretofore proposed for either detergent or antiwear purposes, it would have been surprising to discover that they were effective for either of these purposes. However, that they possessed not one but both of said qualities was altogether unexpected and could not have been predicted.

The polymeric additives of the present invention are copolymers of (A) one or more oil-solubilizing compounds having a polymerizable ethylenic linkage (=C=C=) and a hydrocarbyl group of from 4 to 30 aliphatic carbon atoms and (B) one or more ;,5-1111821111- ratelrld monocarboxylic acids of from 3 to 8 carbon atoms eac Representative copolymers coming within the scope of the present invention are for example those of dodecyl methacrylate with methacrylic acid; diisobutylene with acrylic acid; Z-ethylhexyl vinyl ether with methacrylic acid; dodecyl methacrylate with crotonic acid; diisobutylene with acrylic acid; hexadecylstyrene with methacrylic acid; and allyl stearatewith angelic acid. The present invention also contemplates the use of copolymers formed from a plurality of one or more of each of the oilsolubilizing and acid monomer components of the polymer. Representative copolymers of this type are, for example, those of diisobutylene and dodecyl methacrylate (both oil-solubilizing monomers) with methacrylic acid;

l-octade'cene and 2-ethylhexyl vinyl ether vwith acrylic a r 4 acid; dodecyl methacrylate with acrylic and methacrylic acids; and dodecyl methacrylate and Z-ethylhexyl vinyl ether with methacrylic and angelic acids.

The oil-solubilizing monomer portion of the polymeric additives of this invention can be any compound having at least one ethylenic linkage C=C together with at least one substituent group which contains an oilsolubilizing hydrocarbyl group of from 4 to 30 aliphatic carbon atoms, and which is characterized by the ability to copolymerize through said ethylenic linkage with the polar monomer referred to above in the presence of a suitable catalyst. Alternatively, the oil-solubilizing aliphatic radical can be introduced into the copolymer, as will hereinafter be more fully described. This aliphatic radical, whether present in the original monomer or introduced into the copolymer, imparts oil solubility to the polymer and is preferably a branched or staightchain alkyl radical or a cycloalkyl radical such as butyl, isobutyl, n-pentyl, n-hexyl, 2-ethylhexyl, decyl, dodecyl, tetradecyl, cyclohexyl, 4-ethylcyclohexyl, or the like, or an alkenyl radical such as oleyl, ricinoleyl, or the like, wherein the ethylenic double bond has substantially no copolymerizing tendency. Oil solubilizing monomers of this general character are well known in the art and are frequently employed as the oil-solubilizing portion of copolymers which are added to lubricating oils to improve the viscosity index and pour point characteristics thereof. They include such materials as olefins and ethylenically unsaturated ethers, esters, ketones, aldehydes, and the like.

The oil solubilizing monomers of component (A) may also be illustrated by the following general formula:

' in which R and R are members of the group consisting of hydrogen and hydrocarbon radicals of from 4 to 30 carbon atoms, at least one of which contains an aliphatic hydrocarbon group of from 4 to 30 carbon atoms as described above, G and G are members of the class consisting of oxy (O), carbonyl and carbonyloxy OLEFINS Octadecene-1 4-0ctylcycl0hexene-1 3-phenylhexadeeene-l Hexene-l Zethylhexene-l Diand triisobutylene Tripropylene p-Octylstyrene Dodecene-l Vinylcyclohexane Hexadecene-l 2-hexadecylbutadiene-l,3

Cyclohexene p-Tertiarybutylstyrcne ETHERS Vinyl n-butyl ether Propenyl Msthylhexyl ether Vinyl Q-ethylhexyl ether Crotyl n-oetyl ether Allyl n-butyl ether Isopropenyl dodecyl ether Allyl isobutyl ether l-decenyl butyl ether Allyl cyclohexyl ether Allyl 4,4,8,8-tetramethyl-d0cosyl ether Methnllyl n hexyl ether Methallyl n-decyl ether Methallyl Z-ethylhexyl ether Methallyl octadecyl ether l-oicosenyl decyl ether Vinyl p-octylphenyl ether Methallyl p-tert. butylphcnyl ether l-deeenyl p-cetylphenyl ether l-decenyl Z-phcnylbutyl other were demonstratedby incorporating the copolymersinto ESTE'RS vi l p q t' oyclohexylmethacryme lubricatmg o1ls.. The lubricant compositions thus b- Vinylpalmrtate Qyclohexyl2-dodecenoate tamedwere tested to determine their detergency andyloleate Decyl vinylacetate d h Allyl caprylate 150mm.mchlomacrylate 5 eposrion properties. T e results of these tests are given fillyllaurate f-Is'oalmlyslrghenzyl i-hiexadece'noate m TableI below.

oea e fii palmitate g g g g f g e In1 the teststhe baseoll, unless otherwise mdlcated, 18 W stearate Methylc clohex l2-eth 1*2- and v r Allyl Z-ethylhexanoate hexengate y y E wag: 30 grade gnnefal hibnv fi% ?%b d gethyldocowl crotonate gating oil aving a viscoslty index of 85 WhlCh is derived y es erso a assu aci s ctadecylisocrotonate 1' Allyl esters of lard acids n-Butyl-Z-eicosenoate cahformawaxy crude' Vanous. 9m? of h fi gl l l y t palm amylphenyl octadecyl copo ymers are lncorporated into the 011 as indicated in e a y caproa e maleate terms of percent by Weight Methallyl naphthenate -Hexadec l len. l 2 1:1 11 l Methanylricinoleate pmaleate ypl y 43 w my The plstonvarnish ratings of the lubricant composi. g -gg tglbenzoate o-fig s -oc y y w t10 ns. were obtained by the standard FL-2 test p'rocedure'- vrl t u cy'dohexane carboxy- .sfi i l maleate 15 as set out 1n the-J une 21, 1948, report of the Coordinating ae 'exaecyrnaeate r Methallylpalmltate Di-methylcyclohexylmaleate Res-efnfll Councll In thls test the lu.bncat1.ng 011 5 grotyi 1 mb Mono-Z-ethylhexylmaleate positions were tested as crankcase lubricants in a 6-cyl1n- .a' aaaztyttatm aztsaataztaz Chevrolet engme, a law-grade gasohne espe- 1-pr0penylnaphthei1ate Di-dodecyl 1I 1esaco11ate clally prone to cause engine deposits. At the end ofeach. BEEfiitfiiittZ iii oifi fiitaitfit yittiifim test i? engmelwfis dlsmanfledfind the deieigemy j iei aae l ethacr laze Monmhexadewlitacomte deposition properties of the lubricant compositions were g gg gg s g lsgggg r y rggg eate. determined by. exam ning the engine deposits on the pis- Allyl3,5-diisobutyl benzoate l-hexadecenyl myristate tonand visually rating them as to the amount of piston Although any of the oil solubilizing compounds varn sh present. The piston varnish ratings of thecom scribed above will give effective copolymer compositions s given In terms on a Smale of for lubricant compositions in accordance with the pres 0 10' w1th 10 representmg the complete absence em invention, higher alkyl esters of mil-unsaturated monodepqslts l carboxylic acids of from 3 to 6 carbon atoms having alkyl The'depo,slt}on charactenstlcs 1u b r1cant comp-051i groups of from 3 to Carbon atoms are most Preferred, trons containing the copolymenc addrtrves were also both for availability and effectiveness of copolymers 30 determined in the lacquer deposition test. In this test: pared from them. Representative acids of this type are tymcaLePgme fuel cowbustlon W? Passed the acrylic, methacrylic, .crotonich tiglictangelici wethyly the lubrlcant compositions and the ability of the lubriacrylic, wmethylcmtonict afethylcmwnich fiethylcmp cant compos1t1 ons to solubllzze and reta n the lacquer-. tonic, fl-propylcrotonic, and hydrosorb-ic cid d h forming materials was observed by we1ghmg the amount like Even more desirable are the alkyl esters f' li of lacquer deposits formed on a fresh 1ron catalytic surand methacrylic acids containing from 10 to 20 carbon face for a standard perlod of time. The lacquer deposit atoms in the alkyl groups since they are, found to of; the lubricant COmPOSItIOH is taken as the number; ofv vide highly superior polymers for the lubricant composimllllgrams P on the metal Surface, y tions of the invention and are obtainable in commercial correlated directly to the piston varnish rating obtained; quantities 40 m the standard FL-Z test procedure outlined-in the above Various copolymers employing representative oil-solu- Paragraphbilizing monomers of the foregoing-types were prepared. Both the test procedllre the lacquer PQS r' to illustrate the oil solubilizing effect of the monomers on test f fully'descrlbefl 111 the dlclosure which the resultant copolymers. The solubility of the copolyfollows with regard to the particular lubricant composimers in oil and their suitability as lubricating oil additives tion ofthe present invention.

Table I Piston. Ratio of varnish (1) monomer Piston Lacquer rating Lubricant composition to (2) varnish deposit (estimonomer rating (millimatedto grams) from monomer lacquer deposit) Base oil alone 3.0 850 2.8% (1) dodecyl methacrylate, (2) N ,N'-di-2-hydroxy-cthyl maleamlde 20/1 450 5.0 2.8% (1) dodecyl methacrylate, (2) allyl stearate, (3) maleic anhydrrde h 20/1/1 405 5.2 1.5% (1) dodccyl methacrylatc, (2) N-(Z-hydroxyethyl) methacrylam1de.. 7/1 6. 3 3.0% (1) tridecyl methacrylate, (2) octadecyl methacrylate, (3) monododecyl ether of hexadecaethylene glycol a methacrylate 10/6/1 8. 4 2.5% (1) allyl stearatc, (2) didodecyl maleate, (3) di-(hydroxyethyl) ethylenediamine salt of monododecyl maleatc t 5/5/2 5. 5 2.8% (1) vinyl ethylhexoate, (2) itaconic acid 15/1 501) 4. 5 2.8% (1) vinyl stcarate, (2) maleic anhydride, (3) monododecyl et one glycol b rncthacrylate, (4) methacrylamide 30/1/2/1 325 6. 0 2.5% (1) allyl stearate, (2) ethylene glycol monooleate monomaleate, (3) mono- N ,N-di(2-hydroxy-ethyl) ethylenediamine maleate (salt) 5/4/1 4. 0 2.8% (1) octadeeene, (2) monododecyl maleate, (3) monopcntaerythritol maleate 2/1/1 500 4.- 5; 2.8% (1) hexane-1, (2) dodecyl methacrylate, (3) methacrylic acid, (4) monododeeyl ether of eicosaethylene glycol methacrylate 25/25/1/4 400 5. 5 2.8% (1) di-Z-ethylhexyl fumarate, (2) octadecene-l, (3) cro onotridecyl ether of decaethyleneglycol d methaorylate 25/25/8/2 570 4. 0 2.8% (1) allylethyl ether, (2) vinyl stearate, (3) itacon odecyl ether of decaethylene glycol d crotonate 14/50/7/3 3.0% (1) vinyl 2-ethylhexyl ether, (2) tetradecylphenyl maleate, (3) dodecyl malcate,

(4) maleic acid 6/3/1/2 4. 6 1.6% (1) dodecyl acrylate, (2) monododecyl ether of decaethylene glycol d acrylate,

(3) acrylic acid 780/9/1 5.6 1.5% (1) hexadecyl styrene, (2) mcthacrylic acid 5.8/1 5. 9

In Neutral Mineral LubricIa ting Oil from solvent-refined waxy-California crude.

Polyethylene glycol of 704 M. Polyethylene glycol of 220 M.W. "Polyethylene glycol of 880 M.W. Polyethyle n e glycol of 440 M.W

From the above test data it will be seen that all of the various oil-solubilizing monomers representative of the aforementioned types were effective in the production of useful, copolymeric lubricating oil additives which are capable of preventing deposits from lubricant compositrons under typical engine operating conditions. These monomers, as previously described, constitute a definite, recogmzed class of compounds which have been used heretofore in the art in the production of polymeric lubricating oil additives of the nonpolar type, such as VI lmprovers and pour point depressants. Although the results demonstrate beyond any reasonable doubt the suitability of the different oil-solubilizing monomers within the terms of the description in the production of oil soluble copolymers, it should be understood that the eflicacy of each individual class of copolymers as detergents is primarily dependent upon the particular polar or functional group in the so-called polar monomer and its relationship to the rest of the copolymer. i

Since the functionality of the individual polar groups differs and is largely empirical in nature, no conclusion is intended to be drawn concerning equivalency of the various copolymeric lubricating oil additives employed as detergents in this illustration. The polar groups of the particular class of copolymers of the compositions of this invention and their balance or relationship to the remainder of the copolymers are more fully discussed in the disclosure which follows, along with additional examples of the invention.

The one-unsaturated monocarboxylic acid monomers of the copolymeric additives employed in this invention have the general formula where the R s, R s and R s, which can be the same as or different from one another, are selected from the group consisting of hydrogen atoms and alkyl groups of from 1 to 4 carbon atoms. Representative acids of this type, any one or more of which can be employed in forming the copolymers hereof, are acrylic, methacrylic, crotonic, tiglic, angelic, u-ethylacrylic, a-methylcrotonic, a-ethylcrotonic, fl-ethylcrotonic, a-butylcrotonic, hydro sorbic and a-ethylhydrosorbic acids, and the like. A preferred group of acids is made up of acrylic and,methacrylic acids.

In preparing the copolymers of this invention, it is necessary that conditions be chosen which will insure copolymerization and the formation of copolymers having the requisite oil solubility. The oil-solubilizing monomers vary somewhat in their solubilizing characteristics, Thus, in some cases, oil-solubilizing/acid (A) and (B) monomer ratios as low as 1:1 can be employed, while in others, ratios as high as about 20:1 can be used in order to obtain a copolymer product having optimum solubility characteristics. However, copolymers having excellent detergent and antiwear characteristics, together with the requisite oil solubility (which is at least 2%, and is preferably greater than by weight of'the lubricant composition) can be prepared by employing oil-solubilizing (A) monomer to acid (B) monomer ratios of from about :1 to 3:1, and such ,a range is therefore preferably employed wherever possible. The copolymers employed in a practice of this invention can be prepared by one or more of a variety of different methods known in the art. Thus, one may simply polymerize a given oil-solubilizing monomer with a given acid to form the desired copolymer. Alternatively, suitable precursor compounds can be employed in the copolymerization reaction, with the desired. monomer components of the copolymer then being formed by the appropirate treatment of the polymerized reaction product. For example, a copolymer of dodecyl methacrylate and methacrylic acid can be prepared by 1) directly cm polymerizing the two monomers; or (2) starting with a homopolymer of dodecyl methacrylate, subjecting the polymer to partial hydrolysis in order to free the desired proportion of carboxyl groups. Other possible variations in the nature of the reactants and in the selection of asuitable reaction path would also suggest themselves to those skilled in the art.

Having selected the desired monomeric reactants, the copolymer of this invention can be prepared by conventional bulk, solution or emulsion methods of addition polymerization in the presence of an addition polymerization initiator. Preferably, however, the copolymerization is effected in an inert organic solvent such as benzene, toluene, xylene or petroleum naphtha in the presence of a free radical-liberating type of initiator such as a peroxy compound, for example, benzoyl peroxide, acetyl peroxide, tert.-butyl hydroperoxide, di-tert. butyl peroxide, di-benz0yl peroxide, or di-tert. amyl peroxide, or an azo initiator such as 1,1-azodicyclohexane-carbonitrile or a,a'-azodiisobuteronitrile. The catalyst, or polymerization initiator, can be employed in an amount of from about 0.1 to 10%, with a preferred range being from about 0.25 to 2%. If desired, the catalyst can be added in increments as the reaction proceeds. Likewise, additional portions of the solvent can also be added from time to time in order to maintain the solution in a homogenous condition. The temperature of copolymerization varies from about 75 to C., with the optimum temperature depending on the solvent selected, the concentration of monomers present therein, the catalyst selected, and the time of the reaction. Much the same conditions prevail when the copolymerization is efiected in bulk rather than in the presence of an inert solvent.

The copolymer additives of the invention have apparent molecular weights as determined by standard light scattering methods of at least 2,000 and preferably at least 8,000. For practical purposes, molecular weights of from 100,000 to 1,000,000 are most suitablefrom the standpoint of viscosity and other physical characteristics of the polymeric additives.

In a preferred application of the copolymeric lubricating oil detergent additives of the present invention in mineral lubricating oil, it has been noted that a certain optimum relationship between the total number of aliphatic carbon atoms to polar groups within the molecule appears to exist. Evidence has been obtained that for a given concentration the copolymer compositions containing a ratio of aliphatic carbon atoms to polar groups within the range of from 50 to 225, preferably 75 to '125, appear to embrace the optimum composition for deposit reduction effectiveness. In determining this ap parent balance between the polar and nonpolar constituents, the aliphatic carbon atoms to be considered are the following: CH CH;;,

and excluding aromatic ring carbon atoms or the carbon atom of the carbonyl groups. As polar groups, the following representative radicals are included: -OH (either acid, alcohol or phenol), NH

l IH, nt-

and an acid anhydride group as a single unit.

Although this concept of copolymer compositions appears to correlate generally with their performance in all of the oils of lubricating viscosity, there may be additional composition factors which alter the efiect of these improving agents in various types of lubricating oil systems and service. However, on the basis of these assumptions, it becomes evident that variations in the aliphatic carbon to polar ratio and hence performance efficacy may be accomplished by the choice of the acid derivative radical and degree of neutralization in the modification of polar component (B).

Typical methods for preparing the copolymers which '9; can be exployed with success as detergents and antiwear oxidants in lubricant compositions are "given in the following examples.

EXAMPLE 1 In this operation a homopolymer of dodecyl methacrylate having an apparent molecular weight of about 20,000 was employed as a starting material from which was prepared a copolymer of dodecyl methacrylate and methacrylic acid. The preparation was as follows: A solution of 14 grams of potassium hydroxide in 300 cc. of 2-ethylhexanol was prepared, and to this solution was added 800 cc. of a 40% solution in mineral oil of the rnethacrylic 'homopolymer, this amount of KOH constituting a slight excess over that theoretically required to effect the desired saponification of approximately 15% ofthe ester groups present in the polymer. The resulting solution was heated to 320 F. and maintained at this temperature, with stirring, for 10 hours. To this solution was then added 50 cc. of benzene along with a 50% excess of 6N HCl over the amount theoretically required to liberate the free carboxyl groups from the corresponding salt. The acidified solution was then reflu'xed for 2 hours, after which it was cooled, diluted with ethyl ether, and water washed (along with a small amount of ethyl alcohol to break the emulsion) until neutral to litmus. The solution was then placed in a steam bath to remove the ether and thereafter distilled in vacuo until a pot temperature of 350 F, at 3 mm. Hg was reached in order to remove the 2-ethylhexanol and the dodecyl alcohol present, leaving as the oil-soluble residue, the desired copolymer of dodecyl methacrylate and methacrylic acid in approximately 7:1 molar ratio.

EXAMPLE II The preparation of the copolymer of dodecyl 'methacrylate with methacrylic acid as described in the fore going example was repeated adjusting the pr'oportio ns of dodecyl methacrylate and methacrylic acid to give the copolymer of dodecyl methacrylate and methacrylic acid in approximately 14:1 molar ratio.

EXAMPLE III Dodecyl methacrylate and acrylic acid were copolymerized in accordance with the procedure outlined in the above examples toproduce the copolymer of dodecyl methacrylate and acrylic acid in approximately 7:1 molar ratio.

EXAMPLE IV 349 g. of mineral oil concentrate containing 40% by weight of hexadecylstyrene and 350 ml. of toluene were introduced to a reaction vessel. The mixture was stirred at about 245 F. and 20 ml. portions of a 5% solution of benzoyl peroxide in toluene were added at approximately hourly intervals over a period of about 24 hours. During this period 68 g. of glacial methacrylic acid dissolved in 370 ml. of toluene was added in approximately the same portions and intervals. The polymeric product was precipitated with acetone and methanol. The product was a copolymer of hexadecylstyrene and methacrylic acid in approximately 6:1 molar ratio.

In general, excellent detergent and antiwear properties can be imparted to lubricating oils by dissolving therein a quantity of from about 0.1 to 10% by weight of the copolymers of the type described above, although a preferred range is from about 0.5 to 5% by weight. The copolymeric additives of this invention can be used with good effect in the case of any one of a wide variety of oils of lubricating viscosity, or of blends of such oils. Thus, the base oil can be a refined Pennsylvania or other paraffin base oil, a refined nap'hthenic base oil, or a synthetic hydrocarbon or non-hydrocarbon oil of lubricating viscosity. As synthetic oils there can be mentioned alkylated waxes andsimilar alkylated hydrocarbons of relatively high molecular weight, hydrogenated polymers of hydrocarbons, and the condensation products of chlorinated alkyl hydrocarbons with aromatic compounds. Other suitable oils are those which are obtained by polymerization of lower molecular weight alkylene oxides such as propylene and/or ethylene oxide. Still other synthetic oils are those which are obtained by polymerization of lower molecular weight alkylene oxides such as propylene and/or ethylene oxide. Still other synthetic oils are obtained by etherification and/or esterification of the hydroxy groups in alkylene oxide polymers such as, for example, the acetate of the 2-ethylhexanol-initiated polymer of propylene oxide. Other important classes of synthetic oils include the various esters as, for example, di- (Z-ethylhexyl) sebacate, tricresyl phosphate and silicate esters. If desired, the oil can be a mixture of mineral and synthetic oils.

While satisfactory lubricant compositions can be obtained by adding to the base oil employed only one or more of the copolyme'ric additives of the type described above, it also falls within the purview of this invention to provide lubricant compositions which contain not only such copolymers, but also other additives such as pour point depressants, oiliness and extreme pressure agents, antioxidants, corrosion inhibiting agents, blooming agents, thickening agents, and/or compounds for enhancing the temperature-viscosity characteristics of the oil. The present invention also contemplates the addition to the lubricant composition (particularly when the amount of copolymer employed is relatively small) of auxiliary detergents and/or antiwear agents.

The efficacy of copolymeric additives of the type described above as detergents and antiwear agents in lubricating oils is illustrated by data from a number of tests. In the tests from which the data is obtained the base oil, unless otherwise specified, is a solvent-refined, wax-free SAE-30 grade mineral lubricating oil having a viscosity index of which is derived from California waxy crude. Various amounts of the copolymeric additives are incorporated into the oil as noted in terms of percent by weight.

In the lacquer deposition test the low temperature detergency of the oils tested is measured by determining the ability of the oil to solub ilize and retain typical engine fuel deposits and precursors thereof which are formed due to incomplete combustion of the fuel. Retention of these deposits in a'given oil depends upon their dispersal and upon minimizing their polymerization to lacquer.

Briefly described, the lacquer deposition test involves condensing fresh c'ool fiame oxidation products from a standard test fuel, simulating the fuel combustion products of an internal combustion engine in a steel vessel containing a certain amount of the lubricating oil being tested. The steel surface of the vessel acts as an iron catalyst for polymerization of the fuel oxidation products to lacquer in the same manner as the steel surfaces in an internal combustion engine. After the oxidation products have been condensed, the steel vessel containing the lubricating oil is heated for 24 hours at a temperature selected to correspond with actual engine conditions. The test oil is then decanted while hot from the lacquer deposits formed in the steel vessel due to polymerization and the lacquer deposits are de-oiled and weighed.

In the actual test a low grade gasoline is employed of the type described in connection with the standard FL-Z test procedure given below. The gasoline at a rate of 13.3 cc. per hour is vaporized and mixed with air, the air r-ate being 1.75 liters per minute. The vapor mixture of gasoline and air is then fed into an elongated cool flame combustion chamber of standard design having a diameter of 1 /2 inches. The cool flame combustion chamber is maintained at 695 F. The test is continued for 1 hour during which the oxidation products issuing from the cool flame combustion chamber are condensed into the weighed steel catalyst vessel which contains 30 g. of the oil being tested at about room temperature. The steel vessel containing test oil and condensed oxidation products is then heated for 24 hours at F. The

oil is decanted from the lacquer deposits in the vessel, following which the deposits are de-oiled by washing with petroleum solvent. The increase in weight of the steel presented in Table III below, when the base oil is compounded with the indicated amounts of a copolymer, greatly superior results are obtained.

Table III Piston Ratio oi (1) varnish Piston monomer Piston Lacquer rating ring Lubricant composition varnish deposit (estiwear monomer rating (miliimeted rate,

to (3) grams) from mgJhr. monomer lacquer deposit) Base oil l n 3. 850 5.0 1.5% (1) dodeeyl methecrylate and (2) methacrylic acid in base oil 7/1 6. 1 2. 4 1.5% (1) dodecyl methacrylate and (2) mothacryiicacid in base oil 14/1 4. 8 3. 6 1.5% (1) dodecyl mcthacrylate and (2) acrylic acid in base o1l. 7/1 5. 3.0 1.5% (1) hexadeeylstyrene and (2) methacrylic acid in base 011... 6/1 5. 9

Table 11 LB PVR LD PVR 140 9. 5 335 o. 0 170 9.0 370 a. 5 190 a. 5 420 5. 0 220 s. 0 480 4. 5 245 7. 5 570 4. 0 27s 7. 0 700 3. 5 305 6.5 850 3.0

The correlated values in the above table provide an accurate means for estimating from the lacquer deposits determined for a given oil the piston varnish rating to be obtained in the standard FL-2 Chevrolet engine test.

In the test where the piston varnish ratings are obtained, a given lubricating oil composition is tested as the crankcase lubricant in a 6-cylinder Chevrolet engine using a low grade gasoline especially prone to cause engine deposits, the condition being those defined in the standard FL-2 test procedure as described in the June 21, 1948, report of the Coordinating Research Council. This procedure requires the maintenance of a jacket temperature of 95 F. and a crankcase oil temperature of 155 F. at 2500 rpm. and 45 brake horsepower of 40 hours, and therefore closely simulates the relatively cold engine conditions which are normally experienced in city driving. At the end of each test, the engine is dismantled and the amount of engine deposits on the piston determined and expressed as the piston varnish rating. This value is obtained by visually rating (on a scale of 0 to 10, with representing the absence of any deposit) the amount of deposit on each piston skirt and averaging the individual ratings so obtained for the various pistons. Under the conditions of this test, a piston varnish rating of 4.5 is indicative of satisfactory performance, though preferably this rating should be 5 or above. The Wear experienced by the piston rings during the test is alsomeasured in certain cases and expressed in mgs. of metal lost per hour. 5 mgs. per hour is regarded as satisfactory, though preferably the loss should be 3 mgs. or less per hour. In the case of the base oil alone without the addition of any additives it is found that the piston varnish rating is approximately 3.0 and the piston ring weight loss is 5.5 mgs./hr. On the other hand, as indicated by the data From the test results of the foregoing table it will be seen that each of the illustrative compositions containing the copolymeric lubricating oil additives according to the invention possess greatly improved lubricating properties compared to the base oil alone.

In the foregoing description of the invention, the term hydrocarbyl is used with reference to the class of organic groups commonly known as hydrocarbon groups. As employed herein, this term is considered to be a more convenient and concise generic expression for describing said hydrocarbon groups.

This application is a division of Lowe, Stewart, and Stuart patent application Serial No. 563,207, filed February 3, 1956, which in turn is a continuation-in-part of Lowe, Stewart and Stuart patent, application Serial No. 328,151, filed December 26, 1952, and now abandoned.

We claim:

1. A lubricant composition comprising a major portion of an oil of lubricating viscosity, together with from about 0.1 to 10% by weight of a copolymer of monomers consisting of (A) a higher alkyl ester of an a e-unsaturated carboxylic acid of from 3 to 6 carbon atoms in which the alkyl group contains from 8 to 30 carbon atoms and (B) an acid having the general structural formula where R R and R are radicals selected from the group consisting of hydrogen atoms and alkyl groups of from 1 to 4 carbon atoms, said components being present in the copolymer in the ratio of from about 3 to 15 monomer units of the ester (A) for each monomer unit of the acid (B) and said copolymer having a molecular weight of at least 2,000.

2. The composition of claim 1, wherein the acid com ponent (B) of the copolymer is acrylic acid.

3. The composition of claim 1, wherein the acid component (B) of the copolymer is methacrylic acid.

4. A lubricant composition comprising a major portion of an oil of lubricating viscosity, together with about 0.1 to 10% by weight of a copolymer of monomers consisting of (A) dodecyl methacrylate and (B) methacrylic acid, said components being present in the copolymer in the ratio of about 3 to 15 monomer units of the ester component (A) for each monomer unit of the acid component (B) and said copolymer having a molecular weight of at least 2,000.

References Cited in the file of this patent UNITED STATES PATENTS 2,653,133 Catlin Sept. 22, 1953 2,737,496 Catlin Mar. 6, 1956 2,800,450 Bondi et al. July 23. 1957 

1. A LUBRICANT COMPOSITION COMPRISING A MAJOR PORTION OF AN OIL OF LUBRICANT VISCONITY, TOGERHER WITH FROM ABOUT 0.1 TO 10% BY WEIGHT OF A COPOLYMER OF MONOMERS CONSISTING OF (A) A HIGHER ALKYL ESTER OF AN A,-B-UNSATURATED CARBOXYLIC ACID OF FROM 3 TO 6 CARBON ATOMS IN WHICH THE ALKYL GROUP CONTAINS FROM 8 TO 30 CARBON ATOMS AND (B) AN ACID HAVING THE GENERAL STRUCTURAL FORMULA 